The present invention relates to the preparation of polymer beads, and in particular, to an apparataus for use in preparing polymer beads which have a relatively uniform particle size.
A wide variety of polymers including polymers of a monovinylidene aromatic such as styrene or esters of an unsaturated carboxylic acid such as acrylic or methacrylic acid esters are prepared in spheroidal bead form using suspension polymerization techniques. Conventionally, suspension polymerization consists of dispersing a monomer as droplets in a vessel equipped with an agitator and containing a continuous phase in which the monomers and resulting polymer are essentially insoluble. The dispersed monomer droplets are subsequently polymerized while maintaining continuous agitation.
Unfortunately, the spheroidal polymer beads prepared by conventional suspension polymerization techniques exhibit a relatively broad particle size distribution. This is generally undesirable for the reason that spheroidal polymer beads employed in most applications advantageously exhibit a generally uniform particle size. For example, the ion exchange resins prepared from copolymer beads of a monovinylidene aromatic and a polyvinylidene aromatic advantageously exhibit a narrow particle size distribution to provide the desired flow characteristics to an ion exchange resin bed comprising said resin. Therefore, a significant percentage of the polymer beads prepared using conventional suspension polymerization techniques possess particle sizes undesirable for their intended application. Such undesirably sized beads are normally wasted or employed in applications of less economic desirability.
Numerous methods are disclosed which propose improved uniformity of polymer beads which are prepared using suspension polymerization techniques. See, for example, U.S. Pat. Nos. 3,728,318; 3,862,924; 2,694,700; 2,932,629; and 3,922,255. Unfortunately, such disclosed methods are not as economical or efficient as would be desirable.
An improved process for preparing spheroidal polymer beads of uniform particle size is disclosed in U.S. Pat. No. 4,444,961. Said process employs an apparatus comprising (1) a monomer reservoir containing a monomer phase comprising a polymerizable monomer, (2) a column containing a continuous phase of a suspending liquid immiscible with the polymerizable monomer or monomer phase and a stabilizing amount of a suspending agent, (3) a monomer jet forming means in intimate contact with the monomer phase and the continuous liquid phase and having an opening connecting the monomer reservoir with the column containing the continuous phase such that the monomer phase passing therethrough into the continuous phase is capable of being a jet having laminar flow characteristics, (4) a vibratory exciter capable of vibratorily exciting the laminar flow jet of the monomer phase such that the monomer jet is broken into droplets and (5) a means for polymerizing the monomer in suspension at conditions such that significant coalescence or additional dispersion of the monomer droplets does not occur.
Unfortunately, the suggested circular geometry of the aforementioned apparatus has a limited capacity for producing large quantities of droplets. It is believed that such limited capacity is the result of radial inflow of the continuous phase of suspending liquid; and mechanical resonances in the piston and vibrator assembly.
In view of the deficiencies of the prior art, it would be highly desirable to provide an apparatus which can be employed in a process for preparing uniformly sized polymer beads wherein said apparatus has a greater capacity for producing droplets (i.e., a capacity for producing large numbers of droplets).